Hydrocarbon exploration and production includes the drilling and monitoring operations. Well boreholes are typically drilled in earth formations to identify and to produce fluids from one or more penetrated formations. During the borehole drilling and the formation production phases, borehole pressures and temperatures are typically elevated necessitating the operation of many types of borehole equipment from within hermetically sealed pressure housings. A variety of measurements are made during and subsequent to the drilling of the borehole. Measured or “raw” data can be transferred from the borehole equipment to the surface of the earth for processing and determining parameters of interest regarding the status of the borehole equipment, the borehole fluid, and the formation material penetrated by the borehole. Alternately, some or even all of the raw data processing is performed downhole, and parameters of interest are transferred or telemetered to the surface of the earth. As an additional option, raw and/or processed data can be stored within the borehole equipment for subsequent retrieval at the surface of the earth. Furthermore, control, calibration, operation and other data are often telemetered from the surface of the earth to the borehole equipment.
Some types of borehole equipment utilize apparatus operating outside of a pressure housing and directly in the high temperature and high pressure environs of the borehole. Such equipment includes, but is not limited to, spinners, calipers, pads, actuating arms, and pistons. Verification of proper operation and positioning of these mechanical devices is essential in a wide variety of borehole exploration and production systems.
As mentioned previously, borehole conditions, including temperature and pressure, are typically harsh. This requires the disposition of selected elements of borehole systems within one or more hermetically sealed housings, commonly referred to as “pressure” housings. Measured data can be recorded by data storage means within the pressure housing for subsequent retrieval. As an example, this methodology is used in certain types of logging-while-drilling (LWD), measurement-while-drilling (MWD). Another example of this methodology is a “slick line” well logging system, wherein borehole instrumentation is conveyed within a pressure housing along the borehole by a non-conducting cable. The pressure housing can also be conveyed along the borehole by means of a cable comprising at least one conductor, such as an electrical or fiber optic conductor. A communication link is thereby established between borehole pressure housing and cooperating equipment at the surface of the earth. This methodology of borehole measurement is commonly known as “wireline” logging. Various borehole exploration and production systems require communication across the pressure/fluid interface defined by the wall of a pressure housing and the harsh borehole environment. Communication requirements can comprise exchange of data between two or more borehole pressure housings, communication between one or more borehole pressure housings and the surface of the earth, or both. Examples of such communication requirements are found in a wide variety of borehole exploration and production systems including MWD, LWD, slick-line logging, production monitoring, certain types of wireline systems using mechanical elements exposed to the borehole environment, and the like.
A primary parameter of interest in the testing and monitoring of hydrocarbon wells is the identification and the measure of components of fluid flowing within the borehole. The primary components are liquid hydrocarbon, water, and/or gas, with secondary components including particulate material such as sand. These measurements are made during initial testing and completion of the well, and subsequently throughout the commercial life of the well.
Early wireline and LWD systems were designed to radially penetrate or “see” into the formation to an extent allowed by the basics physics of the particular system. It has also been found that significant information regarding the type of formation fluid, and parameters such as rock mechanics affecting the production of the fluid, can be obtained from very shallow radial measurements including “images” of the borehole wall. Images can be “maps” of a variety of physical properties such as resistivity, density, elemental concentrations, and the like. Certain types of borehole imaging measurements are most effectively made while drilling or subsequent to drilling using LWD and wireline systems, respectively.